Index: firmware/App/Monitors/Pressures.c
===================================================================
diff -u -rf979c391268b595e44fb6747d43487e4d2294e68 -r9554044bb0ef104eedf8034ac59e1322a52118c5
--- firmware/App/Monitors/Pressures.c	(.../Pressures.c)	(revision f979c391268b595e44fb6747d43487e4d2294e68)
+++ firmware/App/Monitors/Pressures.c	(.../Pressures.c)	(revision 9554044bb0ef104eedf8034ac59e1322a52118c5)
@@ -51,6 +51,8 @@
 /// Pressure Limit minimum stabilization time before short stabilization time activation
 static const U32 PRES_LIMIT_MIN_STABILIZATION_TIME_IN_MS = ( PRES_LIMIT_STABILIZATION_TIME_MS - PRES_LIMIT_SHORT_STABILIZE_TIME_MS );
 
+#define PSI_TO_MMHG                         ( 51.715F )                                    ////< Conversion constant for PSI to mmHg
+
 #define VENOUS_PRESSURE_MIN_PSI             ( -30.0F )                                      ///< Minimum of scale for venous pressure sensor reading (in PSI).
 #define VENOUS_PRESSURE_MAX_PSI             ( 30.0F )                                       ///< Maximum of scale for venous pressure sensor reading (in PSI).
 #define MIN_VENOUS_PRESSURE_FOR_RAMP_MMHG   ( 0.0F )                                        ///< Minimum venous pressure during blood pump ramp up (in mmHg).
@@ -557,7 +559,7 @@
     filterBaroPressureReadings( fpgaBaroPresPSI );
 
     // Get latest dialysate pressure so we can calculate TMP
-    tmpPressure.data = getLongFilteredVenousPressure() - getDialysatePressure();
+    tmpPressure.data = ( getDialysatePressure() * PSI_TO_MMHG ) - getLongFilteredVenousPressure();
 
     // Handle pressure limits state machine
     execPressureLimits();